Method of manufacturing metal bonded abrasive gear hones



o. w. DANIEL 3,494,752

IETHOD 0F IANUFLCTURING METAL BONDED ABRASiVE GEAR n1 Feb. 10, 1970 edMarch 4, ibsa United States Patent 3,494,752 METHOD OF MANUFACTURINGMETAL BONDED ABRASIVE GEAR HONES David W. Daniel, Birmingham, Mich.,assignor to Lear Siegler, Inc., Santa Monica, Calif., a corporation ofDelaware Continuation-in-part of application Ser. No. 313,240, Oct. 2,1963. This application Mar. 4, 1968, Ser. No. 721,535

Int. Cl. B24d 3/08 US. Cl. 51-293 27 Claims ABSTRACT OF THE DISCLOSURE Ametal bonded gear hone is provided by dissipating an interim binder,leaving behind on the surfaces of gear teeth a mixture of abrasiveparticles bonded together and bonded to the gear teeth by metal.

CROSS-REFERENCE TO RELATED APPLICATION The present application is acontinuation-in-part of my prior copending application, Ser. No.313,240, filed Oct. 2, 1963, and now abandoned.

FIELD OF THE INVENTION The present invention relates to gear honingtools in the form of a metal gear having the surfaces of the teethprovided with abrasive particles supported and bonded to the toothsurfaces of the tool by metal. Hones of this type have been made by aprocess in which a mixture of molten metal and abrasive particles issprayed on the teeth. This is very inaccurate and does not lend itselfto careful control of tooth profile.

SUMMARY OF THE INVENTION The present invention is characterized in allembodiments by the use of an interim binder. By this term is meant abinder which may be applied in fluid form as a molded coating to teethof a metal gear so that it may be molded into accurately controlledshape and then caused to set. The article may then be removed from themold and the cured binder will retain its molded shape.

In one embodiment of the invention the binder, when it is applied influid form to the teeth of the gear in a surrounding mold cavity,contains a minimum amount of interim binder and is composed for the mostpart of a mixture of metal powder and abrasive particles. After removalfrom the mold the coated gear is heated to melt the metal and to causethe interim binder to be dissipated.

In an alternative method the material cast as a coating on the teeth ofthe gear is a mixture of abrasive particles and the interim binder.After the interim binder has been hardened the gear is removed from themold and the metal is provided adjacent the edge of the teeth. The gearis now heated, causing the interim binder to be dis sipated and causingthe metal to melt and flow into the voids in the coating which remainson the teeth of the gear.

Best results have been obtained when the interim binder is polyvinylalcohol, hereinafter referred to simply as PVA. However, generallysimilar results are obtainable using sodium silicate as the interimbinder, and satisfactory results have been obtained using an aqueouspaste formed of spun silica sold under the trade name Cabosil. Thismaterial is produced by finely dividing and condensing melted silica andappears as extremely small White flakes. The material is a thixatropicagent and produces, when employed with the abrasive particles or themixture of abrasive particles and metal powder, a mixture which may behardened.

It is accordingly an object of the present invention to provide a methodof making metal bonded hones characterized particularly in theemployment of an interim binder which permits casting a coating on theteeth of a gear to exact form followed by a subsequent step of heatingthe cured or hardened binder to cause it to be completely orsubstantially completely dissipated from the tooth coating.

More specifically, it is an object of the present invention to provide amethod of producing the hone described in the preceding paragraph whichcomprises centering a metallic blank with respect to a mold having therequired tooth configuration, with the flanks of the tooth surfaces ofthe mold and blank spaced apart a uniform distance, as for example about.020 inch, thereafter tightly packing abrasive particles within thespace leaving voids as determined by the size and shape of theparticles, thereafter saturating or wetting the assembly of abrasiveparticles between the mold and metal blank with an interim fluid bindersuch for example as a solution of polyvinyl alcohol, baking the completeassembly to solidify the binder, thereafter withdrawing the blank withits tooth flanks coated with the baked mixture of binder and abrasiveparticles, positioning the metallic matrix or brazing material on thecoated blank adjacent the coated tooth flank surfaces, and finallyheating the assembly to a temperature, for an interval of time, and in acontrolled atmosphere sufficient to eliminate the interim binder, tomelt the metallic matrix material, and to cause the matrix material toflow into the voids between the closely packed abrasive particles leftby the elimination of the interim binder thereby brazing the abrasiveparticles to each other and to the metal blank.

It is a further object of the present invention to provide a method asdescribed in the preceding paragraph in which, in order to produce amore closely packed array of abrasive particles, a mixture of abrasiveparticles of different sizes is employed.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the abrasive particles are tungstencarbide.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the spacing between the confrontingflank surfaces of the mold and blank are separated by approximately .020inch and completely fill the spaces between the confronting tooth flankswith abrasive particles, approximately four parts by Weight of theparticles having a grit size of at least and one part by weight of theparticles having a grit size of 270 or less.

It is a further object of the present invention to provide a method asdescribed in the foregoing which comprises the steps of washing theabrasive particles, preferably in carbon tetrachloride, prior tointroducing them into the space between the tooth flanks of the mold andblank in order to improve bonding between the abrasive particles and thebinder.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the matrix material is in wire format the upper surface of the blank directly adjacent to the bottoms ofthe spaces between adjacent teeth thereon.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the metal matrix material ispositioned on a side surface of a coated blank in the form of wiresegments, retaining the segments in place by metallic paste.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the metallic matrix material is atleast principally formed of copper and preferably is "in the form of acopper alloy of approximately 94-95% copper and'the remainder preferably tin.

It is a further object of the present invention to providea method asdescribed in the foregoing in which the interim binder is eliminated andthe metallic matrix material is melted by heating the assembly in asealed retort in the presence-of hydrogen gas.

It is a further object of the present invention to provide a method asdescribed in the foregoing in which the fluid interim binder is appliedby differential pressure and is caused to How into and through voidsbetween the abutting abrasive particles packed in the space betweenconfronting surfaces of tooth flanks of the mold and blank.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawing illustrating preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERREDEMBODIMENTS In recent years a new practice in the finishing of workgears known, as honing has achieved very considerable commercialimportance. The honing of gears is carried out by rotating a work gearin mesh, preferably at crossed axes, and in pressure contact with agear-like honing tool while providing a relative traverse between therotating gear and honing tool in a direction which occupies a planeparallel to the axes of both the gear and tool so as to distribute thehoning action from end to end of the gear teeth. Best results have beenobtained when the hone has its tooth portion formed of a relatively hardbut slightly yieldable and highly resilient plastic material. Epoxyresin has so far proved to be the most efficient material for thispurpose. The resin has embedded therein a multiplicity of abrasiveparticles, these particles being separated and thus capable of relativemovement and independent yielding.

Efforts have been made to produce honing tools which, while of inferioraccuracy, are relatively inexpensive and are satisfactory for removingthe worst of nicks and burrs appearing on finished gears as a result ofmishandling. Honing tools of this nature have been made by spraying amixture of metal and abrasive particles onto the flanks of gear-likeblanks where the sprayed metal adheres to the metallic tooth surfaces.With this method it is of eourseimpossible to maintain anything likeexact tooth form on the finished tool.

With this background, applicanthas developed a method of producing ahone in which abrasive particles are bonded by metal to the tooth flanksof a metal gear-like blank, and to provide this metal bonded abrasivematerial so as to control the final tooth form with exceptionalaccuracy, and tocontrol the thickness of the deposited abrasivematerialwith a corresponding accuracy. Such a hone is illustrated inFIGURE 1, comprising the metal gear-like body having teeth 11 of reducedchordal thickness and provided on the flanks thereof with a layerindicated at 14 composed of a solid array of abrasive particles havingvOids' formed therebetween as a result of irregular size and shape ofthe abrasive particles, the voids being completely or at leastsufliciently filled with a metallic matrix to bond the particles inplace.

Briefly described in general terms, the method has been successfullycarried-gout in the following steps: A steel blankis hobbed intogearform provided with teeth-having a chordal thickness of approximately.040 inchless than the ultimate desired chordal thickness'on thefinished tool. If the honing tool is relatively fine pitch the outsidediameter of the blank is reduced by a small amount as for example, .002inch, so that the metal matrix which subsequently bonds the abrasiveparticles to the flanks of the teeth will span the crests of the teeth.The tooth surfaces to which the abrasive material is to be applied arethen shot blasted on the profiles of the teeth and on the edges of thegear for about an inch back from the roots of the teeth. Excellentresults are obtained when this shot blasting is carried out with 120grit chilled shot using pounds pressure. This shot blasting breaks upthe smooth surfaces and facilitates the flow of the melted metallicbonding material or matrix during the final operation. It also reducesheat reflection from the blank, thus speeding up heating of the blank.

An epoxy mold is provided having the exact desired final configurationof the hone and the tooth surfaces of the mold are waxed or providedwith some other suitable parting agent. The steel blank is positioned inthe mold in properly centered relation. For this purpose the mold andblank may conveniently be supported on apparatus of the type illustratedin Daniel Patent 3,059,278 so that the blank and mold are in exactconcentricity. At this time, due to the initial dimensions of the steelblank, there will appear a uniform space between the confrontingsurfaces of the flanks of the teeth of the blank and the mold ofapproximately .020 inch. As previously stated, this space inasubstantially reduced amount may extend across the crests of the teethof the blank. Preferably, the steel blank has its teeth hobbed to adepth such that a substantial space extends across the crests of theteeth of the mold adjacent the roots of the teeth of the blank and thisspace may be of a thickness comparable to that appearing between thetooth flank surfaces.

The assembly as just described, is now subjected to vibration andconveniently, this may be accomplished by supporting the assembly on atable which is rotated and vibrated. Excellent results have beenobtained when the vibration is at a rate of about 5000 cycles perminute.

During vibration abrasive particles are now introduced into thecontinuous space between the tooth profiles of the blank and those ofthe mold. The eXact size of the particles and the material of theparticles may be varied. However, particles of tungsten carbide exhibitsuperior qualities and adherence in conjunction with the availablemetallic matrix materials, and accordingly, it is preferred to useabrasive particles of this material.

Better adherence or bonding between the interim binder and particles'isobtained if the particles are washd to remove fine dust therefrom. Bestresults have been obtained by washing the particles with carbontetrachloride. It is found that particles which appear to be perfectlyclean and of uniform size, nevertheless when washed in carbontetrachloride give up a quantity of finely divided material suificientto discolor the carbon tetrachloride very appreciably, thusdemonstrating the desirability of this step.

It is essential to have the abrasive particles packed as tightly withinthe narrow space provided as is physically possible. It will of coursebe appreciated that since these particles are of irregularconfiguration,when they are tightly packed into the space there nevertheless remains amultiplicity of voids between the adjacent and contacting particles, thetotal volume of voids being of course dependent upon the size and shapeof the particles. However, it is found that a denser packing of theparticles is possible, thus facilitating the filling of voids by themetallic matrix, as will subsequently be described, when a mixture ofparticles of predetermined different sizes is employed. The principleexplaining this phenomenon is of course obvious since it will beapparent that relatively small particles can occupy voids formed betweenrelatively large particles without increasing the volume occupied by therelatively large particles.

Excellent results are obtained using approximately two parts by weightof tungsten carbide particles of 140 grit size, two parts by weight of170 grit size, and one part by weight of 270 grit size. The smallerparticles evidently occupy voids between adjacent larger particles tosome degree, thus increasing the density of pack of the abrasiveparticles.

It may be noted that efforts to force the particles mechanically intothe narrow space have met with no success since an attempt to force theparticles into the space simply jams the particles and insures that thespaces will not fill.

As an alternative to filling the confined spaces by employing vibration,it is possible to entrain particles in an air stream moving through theconfined space in conjunction with means equivalent to a screen at theopposite side or end of the space to permit passage of air but to arrestmovement of the entrained particles.

Following the step of filling the confined spaces between the flanks ofthe teeth of the mold and blank as completely as possible, there followsthe step of providing a fluid binder for the particles. This binder mustbe fluid so that it may be sucked or applied under pressure so as tocompletely wet all abrasive particles and the metal body in the coatingarea. It also must have the property of hardening sufficiently uponmoderate baking to provide a firm coherent layer adhered sufficientlystrongly to the flanks of the teeth of the blank to permit withdrawal ofthe blank with the coating intact from the mold.

Finally, it is desirable for the binder to have the prop erty, uponbeing subjected to an elevated temperature for a sufficient interval, tobe completely eliminated while a metallic matrix melted under a highersequentially applied temperature flows in to replace the binder materialthus eliminated.

For this purpose it is desirable to select a material which can becompletely eliminated by the application of heat and therefore organicbinders appear preferable. It is selected from materials which aresufficiently fluid at normal room temperatures to permit applicationconveniently to the array of packed abrasive particles. It must bakeunder moderate heating to provide a relatively hard layer which canthereafter be substantially completely eliminated by increasedtemperatures from the voids. Thereafter, while the particles retaintheir accurately formed condition, the metallic matrix material meltsand flows by capillary action and otherwise into the voids betweenabrasive particles.

The material which appears to conform most closely to the foregoingphysical requirements is an aqueous solution of polyvinyl alcohol,commonly identified as PVA. However, satisfactory results have beenattained using sodium silicate solution available commercially as waterglass.

The next step in the manufacture of metal bonded hones is to paint thePVA solution over the upper edge portions of the blank in a continuousannular zone therearound including the roots of the teeth and somewhatradially inwardly therefrom. This wets the surface and permits a laterapplication of the PVA solution to flow more readily completely aroundthe blank.

In the application of the PVA solution to wet the closely packedabrasive particles, the fluid binder may be supplied to the uppersurface and sucked through the packed array of abrasive particles by theapplication of suction therebelow. However, a quicker andbetter controlof the flow of the binder material is obtained when a pressure ring 20is provided which includes radially inner and outer sealing O-rings 22and 24. The pressure ring 20 is clamped concentrically over the metalblank 10 and the mold 26. The mold 26, as disclosed in the prior Danielpatent previously referred to, is carried by a mold ring 28 which iscentered on a pilot 30' provided on the support 32. For the presentoperation shims indicated at 34 are positioned between the top of thepilot 30 and the blank 10 to provide for flow of binder material. Shimshaving a thickness of .001 inch are satisfactory.

The pressure ring 20 is provided at its lower side with a continuousdownwardly facing annular groove or channel 36 of a width sufiicient tooverlie the space defined between the teeth of the mold 26 and the blank10. Liquid binder material is introduced into the channel 36 through afitting 38 and excellent results have been obatined when the liquidbinder material is applied under a pressure of approximately 20 psi. Theapplication of fluid binder material is continued until the bindermaterial is visible through bolt holes 40 present in the blank. Withthis arrangement it is found that the packed assembly of abrasiveparticles can be filled or completely wetted with binder material in ashort interval, as for example, two or three minutes.

The assembly of the mold ring 28, the mold 26, the blank 10, the support32, 30, the abrasive particles, and the binder material is baked forapproximately eight hours at 220 degrees Fahrenheit. This has the effectof causing the PVA to dry thoroughly and to set so as to form a strongself-supporting mixture of particles and binder on the surfaces of theteeth.

The baking operation is conveniently carried out in a combined heatingand refrigerating chamber so that upon completion of the baking cyclethe chamber is subjected to a reduced temperature as for example,approximately 50 degrees Fahrenheit. This causes the epoxy mold to beperfectly rigid and to insure that the coating made up of the abrasiveparticles and the binder is hard and solid.

Thereafter, the support 30, 32 is removed from the mold assembly, theblank is pressed out of the mold, and the abrasive material and binder,which separates freely from the mold surfaces due to the provision ofthe parting agent supplied, remains firmly bonded thereto. It is foundin practice that at this time the abrasive coating is smooth andgenerally continuous, even including sharp two-surface and three-surfacecorner intersections. Dimensional and profile checks of the coated blankat this time conform with remarkable closeness to similar checks of themaster used for the initial formation of the epoxy mold.

At this time the problem is to eliminate the organic binder and toreplace it with a metal matrix which will permanently bond the abrasiveparticles together and to the tooth surfaces of the hone. It has beendetermined that adequate bonding to produce highly useful hones resultsfrom the use of pure copper. This copper may be applied in the form of apaste or it may be applied in the form of a wire, or sections of wiredistributed in a circle around the upper surface of the hone assemblysubstantially at the roots of the teeth. Where wire is employed ratherthan paste, it is desirable to employ sufficient paste in conjunctionwith the wire to retain it in proper position.

In FIGURE 3 there is shown a fragmentary section of the blank 10 towhich the coating of abrasive particles and binder is applied, asindicated at 42. At this time the blank 10 is positioned flat on asupport 44 and on its upper surface is provided the metal wire 46 whichextends around the blank substantially at the zone of the roots of theteeth. The wire 46 is retained in this position by suflicient metallicpaste 48 to fit it in position.

In order to reduce flow of the melted copper or brazing material overthe entire upper surface of the blank,

a-mask 49 is provided. This mask is formed by painting or otherwiseapplying a stop which has the function of acting as a barrier againstflow of the melted cuprous material. Stops having this function areavailable on the open market. A suitable stop for this purpose is soldby McKesson &Robbins under the trade name Merco identified as a coppermask material type A.

Instead of employing copper and a copper brazin paste, a hone havingsomewhat improved wearing properties is obtained by using a metallicmatrix material which is essentially nickel. This material is availablefrom Wall Colmonoy Company in powered form, essentially a powderednickel alloy in which nickel is the principal metallic material. Inusing this material the powdered nickel alloy was mixed with PVA andhardened to produce a solid body from which pieces were cut equivalentto wire segments of the type employed in the use of copper.

When employing the powdered nickel alloy the tooth spaces of the honeassembly were completely filled with the nickel alloy and after thefinal heat treatment, subsequently to be described, it was desirable insome cases to perform a second operation in which additional nickelalloy powder was packed into the tooth spaces of the hone so as tocomplete filling of the voids between abrasive particles.

Finally, the best results have been obtained when the metallic matrixmaterial is employed in wire form and comprises an alloy ofapproximately 94.3% copper, tin, .2% phosphorous, and .5% othermaterials. In the production of hones having a pin size diameter ofapproximately 8% inches this wire is employed at Ma inch diameter and iscut so as to provide lengths extending approximately 90 degrees aroundthe zone of the root diameters of the hone. This wire is retained inplace by a copper brazing paste.

The final operation, which will of course vary slightly in accordancewith the particular metallic matrix material employed and may alsorequire variation in accordance with the density of pack of the abrasiveparticles and for other reasons, is heating to a temperature and for aperiod suflicient to eliminate the organic binder, to melt the metallicmatrix material, and to cause the melted matrix material to flow bycapillary action or otherwise into the voids left by the elimination ofthe binder.

In the case of the hone using the nickel alloy as the metallic matrix,the hone was heated to 1900 degrees Fahrenheit over an interval of about45 minutes and was held at 1900 degrees Fahrenheit for. approximately 30minutes.

Heating was in a retort and a hydrogen atmosphere was supplied duringthe high temperature portion of the heat treatment.

The apparatus for soaking the hone assembly at a high temperature in acontrolled atmosphere is illustrated in FIGURE 4. In this figure thereis shown a retort 50 having a grate 52 adjacent its bottom and providedwith an open top. Surrounding the retort near its open top there isprovided an outwardly extending flange 54 with an upturned edge portion56 defining a channel 58 which in use is filled with sand to provide aseal.

A cover 60 is provided for the retort including a downturned peripheralflange 62 adapted to enter into the sand received in the channel 58. Thecover 60 includes a tubular well 64 for the reception of a thermocouple.A tubular fitting is provided as indicated at 66 for connection to meansfor supplying the purging gas and connects internally to a tube 68dumping into the bottom of the retort below the grate 52. The honeassembly to be heat treated is positioned on the grate and theatmosphereis controlled by admission of gasthrough the ffitting 66, the gascontinuously escaping through the sand seal. When employing a hydrogenatmosphere, air is purged from the retort by first causing nitrogen toflow therethrough and the flow of'hydrogen is not initiated until alloxygen has been expelled and preferably, a substantial increase; intemperature in the retort has been notedv-For example, in practice,nitrogen was shut off when-the temperature; as observed by thethermocouple was 1300 degrees Fahrenheit, after which hydrogen wasstarted through the retort at a flow of about ten cubic feet per hour.

The. method so far described in. detail involves the formation of anassembly. ofabrasive particles between tooth surfaces .of'a blank orcore member and covering tooth surfaces of a mold. Where the hone is inthe form of a fine pitch gear, as for example a gear having adiametrical pitch of 32, the size of the teeth precludes the formationof a coating thereon. In this case the blank may be provided in the formof a steel cylinder having a smooth cylindrical outside diameter. Thisblank is positioned concentrically in a mold, the inner surface of whichis formed to the exact tooth contour desired in the finished mold. Theoutside diameter of the blank is slightly smaller than the insidediameter of the mold so that when the spaces therebetween are completelypacked with abrasive particles, the particles form the entire toothstructure of the hone and provide a continuous connection between theteeth. A hone constructed in accordance with the foregoing isillustrated in FIG- URE 5-where a portion of the cylindrical blank isillus trated at 70 and the abrasive grains received in or bondedtogether by the metal matrix are indicated generally at 72. In this caseit will be observed that the teeth 74 are so small that it would not bepractical to attempt to form them by providing a coating on similarlyshapedteeth on the core 70.

In the application of the interim binder such as PVA or sodium silicate,it has been found that the amount of the binder material received in theclosely packed abrasive particles is not highly critical. It appears tobe perfectly satisfactory to apply the binder in such a way as to insuresubstantially complete filling of all voids in the abrasive particles bythe binder material. However, it has been found that blowing execessmaterial from the voids, or accomplishing similar results by theapplication of suction, does not impair the effectiveness of theoperation. Evidently, if the bonding material thoroughly wets theabrasive grains so that it is present at points of contact betweenadjacent grains, the bonding action is sufiicient. The presence ofexcess bonding material, filling the voids is not objectionable but itapparently is not required.

The quantity of the metal matrix which is caused to flow into the porousassembly of abrasive grains is also not critical. It is of courseessential that the melied metal matrix flow in such a way as to producea metallurgical and/or firm mechanical bonding or interlock ing of allabrasive grains. However, this appears to be accomplished whilesubstantial voids may remain in the abrasive material. Thus, it isapparently sufficient if enough of the melted matrix material flows intothe assembly of abrasive grains to insure that all grains are connectedby the matrix 'to the adjacent grains or to the adjacent surface of thecore. On the other hand, there appears to be no'objection to providingthe metal matrix. in a quantity sufficient to effect substantiallycomplete filling of the voids.'It has been noted that the metal matrixmaterial may be provided in successive steps so that if insufficientmetal matrix material is provided in the first operation, additionalmetal matrix material may be added in a subsequent operation.Alternatively, it has been noted thatjif initially excess metal matrixmaterial is provided, the material apparently completely fills allvoids. in'the assembly of abrasive grains and an excess materialmayaccumulate in spaces between the teeth of the hone or at the undersideof the hone. This excess material maybe removed mechanically and thehone again subjected to the heating operation which may have the effectof permitting additional metal matrix material to bleed out of theabrasive assembly.

The foregoing method depends for its success upon the rather surprisingability to retain the abrasive particles in the shape applied thereto bythe mold as a result of the presence of the interim binder therein, andthereafter, while the core with the applied abrasive material isseparated from the mold, causing the melted metal matrix material toflow into voids between the abrasive grains. When the interim bindermaterial is PVA, this binder material is substantially eliminated duringthe heating of the hone assembly to the temperature sufficient to insurethe melting of the metal matrix material. Nevertheless, the binder orits residue is effective to retain the abrasive grains against shiftingat this time and to preserve the accurately conformed surface profilesof the teeth. It has been found that the present method enables theproduction of hones in which the teeth are Within one or two thousandthsof an inch of predicted dimensions, and in which the tooth profile iswell within accepted limits.

In some cases it is desirable to employ a different metal for bondingthe abrasive particles together and for bonding them to the surface ofthe gear teeth. A metal particularly suitable for this purpose is achrome nickel alloy available under the trade name Nicrobraze. Thismaterial contains approximately 6%% chromium, 4.5% silicon, 3% boron,2.5% iron, 1.5% copper, and the balance nickel. This material is notavailable in wire form and hence the method as previously described isnot available when using this material as the metallic binder. However,it is possible to employ a method which retains the advantages inherentin the use of the interim binder, as will now be described.

In carrying out this method of powdered chrome nickel alloy and abrasiveparticles is mixed with the interim binder, preferably PVA, and the PVAis provided only in sufiicient amount to permit the mixture to beformed. The material is then formed into a thin coating which is dried,and thereafter broken up, ground and sieved to provide a mixture ofparticles somewhat coarser than the abrasive particles which are 140200mesh, and coarser than the powdered metal which is 60-80 mesh. Theproportion of the metal binder to the abrasive particles, normallytungsten carbide, is approximately 3/2.

This powdered material containing both the metal and the abrasiveparticles is packed into a mold surrounding the teeth of a metalgear-like body to provide a coating which may be approximately .020 inchthick. This material after it has been packed tightly into the mold issaturated by adding liquid PVA, after which the material is heated tocause it to set and is removed from the mold.

Thereafter, the metal body with the coated teeth is heated to atemperature suflicient to melt the powdered metal and to completelydissipate the interim binder. The metal forms a matrix ruggedlysupporting the abrasive particles and forming a layer which ispermanently and solidly bonded to the surface of the teeth of the gearbody. Moreover, while the interim binder has been dissipated, it isfound that the metal bonded coating is substantially impervious. Mostimportant however, it is found that the surface configuration of themetal bonded hone after the interim binder has been dissipated and themetal melted to bond the abrasive particles and cooled to final form, issubstantially identical to the tooth surface of the mold in which thecoating was initially shaped.

The present method produces an abrasive coating in which the abrasiveparticles are in contact with each other, thus establishing astructurally continuous material with direct particle-to-particlecontact. Due to the memner of filling the confined spaces between thecore and the tooth surfaces of the mold, the abrasive particles are asclosely packed as possible and an abrasive coating of uniformcomposition is obtained. Thus, as the material of the hone teeth wearsaway during the finishing of a multiplicity of gears, the materialremains always in its effective honing condition with as many aspossible abrasive particles always exposed in the operating surfacesthereof. Moreover, the abrasive surface is a strong hard surface and theabrasive material is characterized by its ability to finish manythousands of work gears in the honing operation.

The drawing and the foregoing specification constitute a description ofthe improved method of manufacturing metal bonded abrasive gear hones insuch full, clear, concise and exact terms as to enable any personskilled in the art to practice the invention, the scope of which isindicated by the appended claims.

What I claim as my invention is:

1. The method of making a metal bonded hone which comprises the step offorming a coating on the surfaces of the teeth of a metal gear-like bodyby filling the space between the teeth of the body and a matching moldwith a mixture comprising an interim binder selected from the groupconsisting of polyvinyl alcohol, sodium silicate, or an aqueoussuspension of spun silica, and abrasive particles, hardening the interimbinder in the mold, removing the gear with the hardened coating from themold, heat ing the body to dissipate the binder from the coating in thepresence of melted metal to cause the metal to be distributed uniformlythrough the remaining abrasive particles.

2. The method as defined in claim 1 in which the interim binder ispolyvinyl alcohol.

3. The method as defined in claim 2 in which the metal is provided inthe form of a powder distributed throughout the mixture of abrasiveparticles and the interim binder, and in which after removal from themold the body with its coated teeth is heated to melt the metal powderdispersed through the mixture.

4. The method as defined in claim 3 which comprises providing the metalin a step which comprises providing a continuous metal filament at thetop edges of the teeth, and in which the metal of the filament is meltedand flows into the mixture of the coating as a result of the applicationof heat which also dissipates the interim bind- 5. The method of makinga metal bonded abrasive tool which comprises: forming a mold having asurface conforming exactly to the required form of the tool, positioninga metal body in juxtaposition to said mold to leave a relatively thincontinuous space therebetween, solidly packing the said space withirregularly shaped abrasive particles and thoroughly wetting the mass ofparticles with a fluid interim binder which in solution wets theparticles and when dried or set retains the particles in aself-supporting state conforming to the shape of the mold after removalfrom the mold, but which may be substantially completely eliminated byheating to a temperature below the melting point of a matrix material,causing the binder to harden while retaining the mass of particles inthe space between the body and the mold, separating the body with theabrasive particles and hardened binder adhered thereto from the mold,applying a metal matrix material selected from the group consisting ofcopper, copper-tin alloy or nickel to the body adjacent the adheredparticles, and heating the assembly to a temperature sufficient first toeliminate the binder and thereafter to melt the matrix material and tocause it to flow into the voids between abrasive particles left by theeliminated binder to provide a permanent metal bond between cbortiguousparticles and between particles and the metal 6. The method of claim 5which comprises heating the assembly as aforesaid in a hydrogenatmosphere.

7. The method of claim 5 in which said body is generally of circularcross-section and said mold is generally annular.

8. The method of claim 5 in which said body is generally of circularcross-section and said mold is in the form of an internal gear.

9. The method of claim 5 in which said body is in the form of anexternal gear and the mold is in the form of an internal gear shaped todefine a space between the flanks of the teeth of the body and mold.

10. The method of making a metal bonded abrasive gear hone whichcomprises: forming a mold having a gear tooth mold surface, positioninga metal body in concentric relation to the mold to provide spacesbetween the tooth flanks of the mold and the body, completely fillingthe spaces with abrasive particles leaving voids therein as determinedby the size and irregular shapes of the particles, thereafter thoroughlywetting the mass of said particles with a fluid interim binder selectedfrom the group consisting of a solution of polyvinyl alcohol or sodiumsilicate which in solution wets the particles and when dried or setretains the particiles in a self-supporting state conforming to theshape of the mold after removal from the mold, but which may besubstantially completely eliminated by heating to a temperature belowthe melting point of a matrix material, baking the assembly to set thebinder, separating the body with the coating of baked binder andabrasive adhered to its teeth from the mold, applying a metal matrixmaterial selected from the group consisting of copper, copper-tin alloyor nickel to the coated body in position to flow into the coating toreplace the binder, and heating the assembly at a temperature and for atime sufficient first to eliminate the binder and thereafter to melt thematrix material and to cause it to flow into the voids in the coating.

11. The method of making a hone as defined in claim which comprises thestep of heatingthe assembly in a hydrogen atmosphere 12. The method asdefined in claim 10 in which the particles are limited to a small numberof distinctly different particle sizes.

13. The method as defined in claim 10 which comprises the step offorcing the fluid binder into the mass of particles by differential airpressure.

14. The method as defined in claim 13 which comprises forming the fluidbinder into the mass of particles until substantially all voids thereinare completely filled.

15. The method as defined in claim 5 in which the hinder is an organicmaterial and which includes the step of eliminating the binder by theapplication of heat during the heating of the assembly to melt thematrix material.

16. Themethod as defined in claim 15 in which the binder is a solutionof polyvinyl alcohol.

17. The method as defined in claim 10 in which the body has teeth ofreduced chordal thickness relative to the teeth of the mold to definespaces of substantially uniform thickness therebetween.

18. The method as defined in claim 10 in which the abrasive particlesare tungsten carbide.

19. The method as defined in claim 10 in which the metal matrix materialis a copper alloy.

20. The method as defined in claim 10 in which the metal matrix materialis a copper-tin alloy.

21. The method as defined in claim 10 in which the matrix material isnickel.

22. The method of making a metal bonded abrasive gear hone whichcomprises: forming a mold having a gear tooth mold surface, positioninga metal body in concentric relation to the mold to provide spacesbetween the tooth flanks of the mold and the body, completely fillingthe spaces with abrasive particles leaving voids therein as determinedby the size and irregular shape of the particles, thereafter thoroughlywetting the mass of said particles with a fluid interim binder which insolution wets the particles and when dried or set retains the particlesin a self-supporting state conforming to the shape of the mold afterremoval from the mold, but which may be substantially completelyeliminated by heating to a temperature below the melting point of amatrix material,

baking the assembly to set the binder, separating the body with thecoating of baked binder and abrasive adhered to its teeth from the mold,supporting the body with its axis vertical from its central portion withits toothed periphery free and unsuppored, applying a metalmatrixmaterial selected from the group consisting of copper, copper-tin alloyor nickel at the top of the body continuously around its periphery justinwardly from the roots of the teeth, and heating the assembly at atemperature and for a time sufficient first to eliminate the binder andthereafter to melt the matrix material and to cause it to flow into thevoids in the coating.

23. The method of making a metal bonded abrasive gear hone whichcomprises: forming a mold having a gear tooth mold surface, positioninga metal body in concentric relation to the mold to provide spacesbetween the tooth flanks of the mold and the body, completely fillingthe spaces with abrasive particles leaving voids therein as determinedby the size and irregular shapes of the particles, thereafter thoroughlywetting the-mass of said particles with a fluid interim binder which insolution wets the particles and when dried or set retains the particlesin a self-supporting state conforming to the shape of the mold afterremoval from the mold, but which may be substantially completelyeliminated by heating to a temperature below the melting point of amatrix material, baking the assembly to set the binder, separating thebody with the coating of baked binder and abrasive adhered to its teethfrom the mold, supporting the body with its axis vertical from itscentral portion with its toothed periphery free and unsupported,applying a metal matrix material selected from the group consisting ofcopper, copper-tin alloy or nickel at the top of the body continuouslyaround its periphery just inwardly from the roots of the teeth, andheating the assembly at a temperature and for a time sufiicient toeliminate the binder from the voids between abrasive particles and tomelt the matrix material and to cause it to flow into and fill the voidsin the coating created by the elimination of the binder.

24. The method of making a metalbonded abrasive gear hone whichcomprises: forming a mold having a gear tooth mold surface, positioninga metal body having a similar gear tooth surface in concentric relationto the mold, the teeth of said body being of reduced chordal thicknessto provide spaces between the tooth flanks of the mold and the body,completely filling the spaces with abrasive particles leaving voidstherein as determined by the size and irregular shapes of the particles,thereafter thoroughly wetting the mass of said particles with a fluidinterim binder which in solution wets the particles and when dried orset retains the particles in a self-supporting state conforming to theshape of the mold after removal from the mold, but which may besubstantially completely eliminated by heating to a temperature belowthe melting point of a matrix material, baking the assembly to set thebinder, separating the body with the coating of baked binder andabrasive adhered to its teeth from the mold, applying a metal matrixmaterial selected from the group consisting of copper, copper-tin alloyor nickel to the coated body in position to flow into the coating toreplace the binder, and heating the assembly at a temperature and for atime sufficient to eliminate the binder from the voids between abrasiveparticles and to melt the matrix material and to cause it to flow intoand fill the voids in the coating created by the elimination of thebinder.

25. The method of making a hone as defined in claim 24 which comprisesheating the assembly in a hydrogen atmosphere.

26.The method of making a metal bonded hone which comprises the step ofpositioning a metal gear-like body within a matching mold to define acontinuous space between the teeth of the body and mold, filling thespace with a mixture of metal particles and abrasive particles, saidmetal particles being formed from a metallic material selected from thegroup consisting of copper, nickel and alloys thereof, thereaftersaturating the mixture With an interim binder selected from the groupconsisting of polyvinyl alcohol, sodium silicate, or an aqueoussuspension of spun silica, hardening the interim binder in the mold,removing the body with the hardened coating from the mold and heatingthe body to a temperature sutficient to melt the metal particles and tosubstantially dissipate the binder to cause the metal to be distributeduniformly through the abrasive particles.

27. The method as defined in claim 26 which cornprises producing themixture of metal particles and abrasive particles by initially Wetting amixture of metal particles and abrasive particles With the interimbinder selected from the group consisting of polyvinyl alcohol, sodiumsilicate, or an aqueous suspension of spun silica, heating the mixtureto form a dry solid material, and breaking up the solid into amultiplicity of particles at least some of which comprise both metal andabrasive.

References Cited UNITED STATES PATENTS Schellens 51-309 Van Der Pyl51-293 Taeyaerts 5 1309 Praeg 5 1298 Decker 5l298 Decker 5 1-298 Harris51295 DONALD J. ARNOLD, Primary Examiner US. Cl. X.R.

